Cyclical deposition of germanium

ABSTRACT

In some aspects, methods for forming a germanium thin film using a cyclical deposition process are provided. In some embodiments, the germanium thin film is formed on a substrate in a reaction chamber, and the process includes one or more deposition cycles of alternately and sequentially contacting the substrate with a vapor phase germanium precursor and a nitrogen reactant. In some embodiments, the process is repeated until a germanium thin film of desired thickness has been formed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Non-Provisional applicationSer. No. 14/135,383, filed Dec. 19, 2013, the disclosure of which isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

Field of the Invention

The application relates to deposition processes for forming germaniumfilms.

Background

Germanium thin films are used in a variety of contexts, particularly inthe semiconductor industry. For example, Ge devices are of interestbecause of Ge high hole mobility. Low D_(it) interface formation withHfO₂ high-k material will allow for good Ge based FinFETs. Germaniumfilms may also be used for epitaxial layers, sacrificial layers and forthe formation of germanides. In many situations, the films are depositedon high aspect ratio structures, such as in the formation of FinFETs.Deposition of relatively pure germanium at relatively low temperaturesby highly conformal processes has heretofore been difficult.

SUMMARY

In some aspects, methods for forming a germanium thin film using acyclical deposition process are provided. In some embodiments, thegermanium thin film is formed on a substrate in a reaction chamber, andthe process includes one or more deposition cycles of alternately andsequentially contacting the substrate with a vapor phase germaniumprecursor and a nitrogen reactant. In some embodiments, the process isrepeated until a germanium thin film of desired thickness has beenformed.

According to some embodiments, after contacting the substrate with avapor phase germanium precursor, the substrate is exposed to a purge gasand/or a vacuum to remove excess germanium precursor and reactionbyproducts from the substrate surface, if any. In some embodiments,after contacting the substrate with a vapor phase nitrogen reactant, thesubstrate is exposed to a purge gas and/or a vacuum to remove excessnitrogen reactant and reaction byproducts from the substrate surface, ifany.

According to some embodiments, the germanium reactant at least partiallydecomposes in each deposition cycle. In some embodiments, the process isperformed at a temperature below the temperature at which the germaniumprecursor decomposes without the presence of another precursor. In someembodiments, the process is performed at a temperature below about 600°C. In some embodiments, the process is performed at a temperature belowabout 500° C.

According to some embodiments, the germanium film is an elementalgermanium film. In some embodiments, the germanium film comprises lessthan about 5 at-% impurities. In some embodiments, the germanium thinfilm contains less than about 3 at-% oxygen. The process of Claim 1,wherein the growth rate is greater than about 2 angstroms/cycle.

According to some embodiments, the nitrogen reactant comprises ammonia,elemental nitrogen, nitrogen plasma, or nitrogen radicals. In someembodiments, the Ge-precursor is a germanium alkoxide or alkylamine. Insome embodiments, the germanium precursor is not a germane. In someembodiments, the germanium precursor is Ge(OCH₂CH₃)₄.

In some aspects, methods for forming a germanium thin film using acyclical deposition process are provided, in which the cyclical processincludes continuously flowing a nitrogen reactant through the reactionchamber, contacting the substrate with a vapor phase Ge precursor,removing excess Ge precursor and reaction by products, if any, from thereaction space by ceasing to provide Ge precursor to the reactionchamber, and repeating the contacting and removing steps until agermanium thin film of the desired thickness has been formed. In someembodiments, the concentration of the nitrogen reactant is kept lowenough to suppress any gas-phase reaction between the nitrogen reactantand the Ge precursor.

In some aspects, methods for forming a germanium thin film using acyclical deposition process are provided, in which at least one of thedeposition cycles includes contacting the substrate with a first vaporphase germanium precursor, exposing the substrate to a purge gas and/ora vacuum to remove excess germanium precursor and reaction by-productsfrom the substrate surface, if any, contacting the substrate with asecond vapor phase reactant, exposing the substrate to a purge gasand/or a vacuum to remove excess nitrogen reactant and reactionby-products from the substrate surface, if any, and repeating thecontacting and removing steps until a germanium thin film of the desiredthickness has been formed. In some embodiments, the second reactant doesnot comprise H₂ or H₂-based plasma species. In some embodiments, thegermanium thin film comprises elemental germanium with less than 5%impurities.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments will be better understood from the appendeddrawings, which are meant to illustrate and not to limit the invention,and wherein:

FIG. 1 illustrates an exemplary cyclical germanium deposition processaccording to some embodiments of the present disclosure.

FIGS. 2A-D show images from a scanning electron microscope (SEM) ofvarious germanium films deposited at different temperatures.

FIGS. 3A and 3B show SEM images of two germanium films deposited at 375°C. and 385° C., respectively.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In one aspect, methods of depositing germanium thin films by a cyclicaldeposition process are provided. In some embodiments a germanium thinfilm is formed on a substrate by a vapor deposition process comprisingone or more deposition cycles in which a substrate is alternately andsequentially contacted with a vapor phase germanium precursor and avapor phase reducing agent, typically a nitrogen reactant. In the firstpart of the deposition cycle, a layer of the germanium precursor formson the substrate surface. In the second part of the deposition cycle,the nitrogen reactant subsequently reacts with the germanium precursorto form a germanium thin film.

In some embodiments the vapor deposition process is an atomic layerdeposition process and the germanium precursor does not decompose.However, in some embodiments the germanium precursor at least partiallydecomposes during the deposition process.

In some embodiments a relatively pure germanium film is deposited by acyclical deposition process. For example, the germanium film may be atleast 90%, 95%, 97%, 98% or 99% pure germanium in some embodiments.

In some embodiments the germanium precursor may be an alkoxide. Forexample, in some embodiments the germanium precursor is selected fromgermanium ethoxide (GeOEt)₄ and tetrakis(dimethylamino) germanium(TDMAGe). Other possible germanium precursors are provided below and mayinclude germanium compounds containing Ge—O bonds, Ge—C bonds (forexample, germanium alkyls), or Ge—N bonds (for example, germaniumalkylamines). In some embodiments the germanium precursor is not ahalide. In some embodiments, the Ge precursor contains a halide in atleast one ligand, but not in all ligands. According to some embodiments,the germanium precursor does not include only germanium and hydrogen.For example, in some embodiments the germanium precursor is not agermane (GeH_(x)).

In some embodiments the nitrogen reactant comprises compounds containingN—H bonds, such as NH₃, nitrogen-containing plasma, atomic nitrogen,and/or nitrogen radicals

In some embodiments, germanium thin films are deposited by alternatelyand sequentially contacting a substrate with Ge(OCH₂CH₃)₄ and NH₃. Insome embodiments germanium thin films are deposited by alternately andsequentially contacting a substrate with tetrakis(dimethylamino)germanium (TDMAGe) and NH₃.

Germanium films may be used in a variety of different contexts. Forexample in some embodiments a germanium film may serve as an epitaxiallayer. In some embodiments a germanium film does not serve as anepitaxial or single-crystal layer. In some embodiments a germanium filmmay serve as a sacrificial layer. In some embodiments a germanium layermay be used for the formation of a germanide. In some embodiments, agermanium layer may be used in a germanium condensation process. In someembodiments a germanium layer may be deposited on a high aspect ratiostructure, such as a FinFET structure. Other contexts in which germaniumthin films may be utilized will be apparent to the skilled artisan. Forexample, germanium thin films may find use in optical applications. Insome embodiments, the germanium films are annealed after the depositionas desired depending on the application.

The cyclical deposition processes disclosed herein allow for conformaldeposition of germanium films. In some embodiments, the germanium filmsdeposited have at least 50%, 80%, 90%, 95% or higher conformality. Insome embodiments the films are about 100% conformal.

The substrate may be, for example, a semiconductor substrate. In someembodiments the substrate surface is H-terminated.

The substrate may be treated prior to depositing the germanium layer.For example, the substrate may be treated with a passivation chemical toprevent oxidation during air exposure prior to depositing germanium. Inother embodiments the substrate is treated to form an interfacial layerprior to depositing germanium.

In some embodiments, following germanium deposition, a further film isdeposited. The additional film may be directly over and contacting thegermanium layer. In some embodiments a metal film is deposited over thegermanium film, for example for forming a metal germanide. Nickel may bedeposited over a germanium layer and subsequently annealed to form anickel germanide. In some embodiments a high-k film is deposited afterthe germanium is deposited. The high-k layer or other film may bedeposited by ALD or by other known deposition methods. In someembodiments, a HfO₂ layer is deposited over the germanium layer. In someembodiments an Al₂O₃ layer is deposited over the germanium layer. Insome embodiments, a deposition process for a film deposited on top of agermanium film uses water as an oxygen source. In some embodiments, adeposition process for a film deposited on top of a germanium film usesozone as an oxygen source. In some embodiments a deposition process fora film deposited on top of a germanium film uses oxygen atoms, oxygenradicals or oxygen containing plasma as an oxygen source.

Cyclical Deposition Process

As noted above, processes described herein enable use of cyclical layerdeposition techniques to deposit conformal germanium layers. Thecyclical deposition process is mostly surface-controlled (based oncontrolled reactions at the substrate surface) and thus has theadvantage of providing high conformality at relatively low temperatures.However, in some embodiments, the germanium precursor may at leastpartially decompose. Accordingly, in some embodiments the cyclicalprocess described herein is a pure ALD process in which no decompositionof precursors is observed. In other embodiments, reaction conditions,such as reaction temperature, are selected such that at least somedecomposition takes place.

Cyclical deposition processes are based on alternatingly providing vaporphase reactants to a reaction space to interact with a substrate surfacecontained therein. Gas phase reactions are avoided by feeding theprecursors alternately and sequentially into the reaction chamber. Vaporphase reactants may be separated from each other in the reactionchamber, for example, by removing excess reactants and/or reactantby-products from the reaction chamber between reactant pulses. Removalmay occur through the use of a purge gas and/or an applied vacuum.

Briefly, a substrate is loaded into a reaction chamber and is heated toa suitable deposition temperature, generally at lowered pressure.Deposition temperatures may be maintained above the temperature at whichthe germanium precursor does not decompose in the presence of anotherreactant and below the germanium precursor's thermal decompositiontemperature. The temperature should also be at a high enough level toprovide the activation energy for the desired surface reactions. Becauseof the variability in decomposition temperatures of different compounds,the actual reaction temperature in any given embodiment may be selectedbased on the specifically chosen precursors. In some embodiments thedeposition temperature is below about 600° C. In some embodiments, thedeposition temperature is below about 500° C. In some embodiments thedeposition temperature is below about 450° C. In some embodiments thedeposition temperature is preferably below about 400° C. and even, insome cases, below about 375° C.

A first germanium reactant is conducted into the chamber in the form ofvapor phase pulse and contacted with the surface of a substrate. In someembodiments the substrate surface comprises a three dimensionalstructure. In some embodiments, conditions are preferably selected suchthat more than about one monolayer of the germanium precursor isadsorbed. Excess first reactant and reaction byproducts, if any, may beremoved from the substrate and substrate surface and from proximity tothe substrate and substrate surface. In some embodiments reactant andreaction byproducts, if any, may be removed by purging. Purging may beaccomplished, for example, with a pulse of inert gas such as nitrogen orargon.

Purging the reaction chamber means that vapor phase precursors and/orvapor phase byproducts are removed from the reaction chamber such as byevacuating the chamber with a vacuum pump and/or by replacing the gasinside the reactor with an inert gas such as argon or nitrogen. Typicalpurging times are from about 0.05 seconds to about 20 seconds, morepreferably between about 1 second and about 10 seconds, and still morepreferably between about 1 second and about 2 seconds. However, otherpurge times can be utilized if necessary, such as when depositing layersover extremely high aspect ratio structures or other structures withcomplex surface morphology. The appropriate purge times can be readilydetermined by the skilled artisan based on the particular circumstances.

Another method for removing excess reactants—metal precursors ornitrogen reactants, reaction byproducts, etc.—from the substrate surfaceor from the area of the substrate may involve physically moving thesubstrate from a location containing the reactant and/or reactionbyproducts.

A second gaseous reactant is pulsed into the chamber where it reactswith the first germanium reactant on the surface to form essentiallypure germanium. The second reactant is a reducing agent that removesligands from the first reactant on the substrate surface. In someembodiments the second reactant is a nitrogen reactant. Excess secondreactant and gaseous by-products of the surface reaction are removedfrom the substrate, for example by purging them out of the reactionchamber, preferably with the aid of an inert gas. The steps of pulsingand removing are repeated until a thin film of germanium of the desiredthickness has been formed on the substrate, with each cycle typicallyleaving more than about a molecular monolayer.

As mentioned above, in some embodiments each pulse or phase of eachcycle may be self-limiting. An excess of reactant precursors is suppliedin each phase to saturate the susceptible structure surfaces. Surfacesaturation ensures reactant occupation of all available reactive sites(subject, for example, to physical size or “steric hindrance”restraints) and thus ensures excellent step coverage. In somearrangements, the degree of self-limiting behavior can be adjusted byadjusting the reaction temperature to allow for some decomposition ofthe germanium reactant in combination with the nitrogen reactant.

In some embodiments the second nitrogen reactant can be providedcontinuously throughout the deposition process. Thus, in someembodiments a nitrogen reactant is flowed continuously throughout thedeposition process and a germanium precursor is provided at regularintervals. In some embodiments nitrogen reactant is flowed continuouslyat a low concentration. The concentration is kept low enough to preventgas-phase reactions between the germanium precursor and the nitrogenreactant thereby maintaining the surface-controlled nature of theprocess.

In some embodiments, a reaction space can be in a single-wafer reactoror a batch reactor where deposition on multiple substrates takes placeat the same time. In some embodiments the substrate on which depositionis desired, such as a semiconductor workpiece, is loaded into a reactor.The reactor may be part of a cluster tool in which a variety ofdifferent processes in the formation of an integrated circuit arecarried out. In some embodiments a flow-type reactor is utilized. Insome embodiments a high-volume manufacturing-capable single waferreactor is used. In other embodiments a batch reactor comprisingmultiple substrates is used. For embodiments in which batch reactors areused, the number of substrates may be in the range of 10 to 200, in therange of 50 to 150, or in the range of 100 to 130.

According to some embodiments, a showerhead reactor may be used.

Examples of suitable reactors that may be used include commerciallyavailable equipment such as the F-120® reactor, F-450® reactor, Pulsar®reactors—such as the Pulsar® 2000 and the Pulsar® 3000—EmerALD® reactorand Advance® 400 Series reactors, available from ASM America, Inc ofPhoenix, Ariz. and ASM Europe B.V., Almere, Netherlands. Othercommercially available reactors include those from ASM Japan K.K (Tokyo,Japan) under the tradename Eagle® XP and XP8. In addition to thesereactors, many other kinds of reactors capable of growth of thin films,including CVD reactors equipped with appropriate equipment and means forpulsing the precursors can be employed.

Suitable batch reactors include, but are not limited to, reactorscommercially available from and ASM Europe B.V (Almere, Netherlands)under the trade names ALDA400™ and A412™. In some embodiments a verticalbatch reactor is utilized in which the boat rotates during processing,such as the A412™. Thus, in some embodiments the wafers rotate duringprocessing. In some embodiments in which a batch reactor is used,wafer-to-wafer uniformity is less than 3% (1sigma), less than 2%, lessthan 1% or even less than 0.5%.

The cyclical germanium processes described herein can optionally becarried out in a reactor or reaction space connected to a cluster tool.In a cluster tool, because each reaction space is dedicated to one typeof process, the temperature of the reaction space in each module can bekept constant, which improves the throughput compared to a reactor inwhich the substrate is heated up to the process temperature before eachrun.

Referring to FIG. 1, and according to some embodiments, a germanium thinfilm is formed by a cyclical deposition process 100 comprising multiplepulsing cycles, each cycle comprising:

-   -   providing a pulse of a vaporized first Ge precursor into the        reaction chamber at step 120 to contact the substrate surface        with the Ge precursor;    -   removing excess Ge precursor and reaction by products, if any,        at step 130;    -   providing a pulse of a second nitrogen reactant into the        reaction chamber at step 140,    -   removing at step 150 excess second reactant and any gaseous        by-products formed in the reaction between the Ge precursor        layer on the first surface of the substrate and the second        reactant, and    -   repeating at step 160 the pulsing and removing steps until a        germanium thin film of the desired thickness has been formed.

As mentioned above, in some embodiments the substrate may be pretreatedprior to beginning the deposition process 100. In FIG. 1 this isindicated by step 110 in which the substrate is optionally subjected toa pretreatment process.

When the Ge precursor contacts the substrate, the Ge precursor may format least a monolayer, less than a monolayer, or more than a monolayer.

In some embodiments, a carrier gas is flowed continuously to thereaction space throughout the deposition process. In each depositioncycle the first germanium precursor is pulsed into the reaction chamber.Excess germanium precursor is then removed from the reaction chamber. Insome embodiments, the carrier gas comprises nitrogen. In someembodiments a separate purge gas is utilized.

The Ge precursor employed in the cyclical processes may be solid,liquid, or gaseous material under standard conditions (room temperatureand atmospheric pressure), provided that the Ge precursor is in vaporphase before it is conducted into the reaction chamber and contactedwith the substrate surface.

“Pulsing” a vaporized reactant into the reaction chamber means that theprecursor vapor is conducted into the chamber for a limited period oftime. Typically, the pulsing time is from about 0.05 seconds to about 10seconds. However, depending on the particular circumstances, includingfor example the substrate type and its surface area, the pulsing timemay be even higher than about 10 seconds.

In some embodiments, for example for a 300 mm wafer in a single waferreactor, the Ge precursor is pulsed for from about 0.05 seconds to about10 seconds, for from about 0.1 seconds to about 5 seconds or from about0.3 seconds to about 3.0 seconds.

The nitrogen reactant may be pulsed for from about 0.05 seconds to about10 seconds, from about 0.1 seconds to about 5 seconds, or for from about0.2 seconds to about 3.0 seconds. However, pulsing times for one or bothreactants can be on the order of minutes in some cases. The optimumpulsing time for each reactant can be determined by the skilled artisanbased on the particular circumstances.

As mentioned above, in some embodiments the Ge precursor is a germaniumalkoxide, for example Ge(OEt)₄ or Ge(OMe)₄. In some embodiments, the Geprecursor is TDMAGe. In some embodiments, the Ge precursor includesalkyl and/or alkylamine groups. In some embodiments the Ge-precursor isnot a halide. In some embodiments the Ge-precursor may comprise ahalogen in at least one ligand, but not in all ligands. The germaniumprecursor may be provided with the aid of an inert carrier gas, such asargon.

In some embodiments the nitrogen reactant comprises a nitrogen-hydrogenbond. In some embodiments the nitrogen reactant is ammonia (NH₃). Insome embodiments, the nitrogen reactant is molecular nitrogen. In someembodiments the nitrogen reactant is a nitrogen containing plasma. Insome embodiments, the nitrogen source comprises an activated or excitednitrogen species. The nitrogen reactant may be a provided in anitrogen-containing gas pulse that can be a mixture of nitrogen reactantand inactive gas, such as argon.

In some embodiments, a nitrogen-containing plasma is formed in thereactor. In some embodiments, the plasma may be formed in situ on top ofthe substrate or in close proximity to the substrate. In otherembodiments, the plasma is formed upstream of the reaction chamber in aremote plasma generator and plasma products are directed to the reactionchamber to contact the substrate. As will be appreciated by the skilledartisan, in the case of remote plasma, the pathway to the substrate canbe optimized to maximize electrically neutral species and minimize ionsurvival before reaching the substrate.

Irrespective of the nitrogen reactant used, in some embodiments of thepresent disclosure, the use of a nitrogen reactant does not contributesignificant amounts of nitrogen to the deposited film. According to someembodiments, the resulting germanium film contains less than about 5-at%, less than about 2-at % or even less than about 1-at % nitrogen. Insome embodiments, the nitrogen content of the germanium film is lessthan about 0.5-at % or even less than about 0.2-at %.

In some embodiments hydrogen reactants are not used in the depositionprocess. In some embodiments, elemental hydrogen (H₂) is not provided inat least one deposition cycle, or in the entire deposition process. Insome embodiments, hydrogen plasma is not provided in at least onedeposition cycle or in the entire deposition process. In someembodiments, hydrogen atoms or radicals are not provided in at least onedeposition cycle, or in the entire deposition process.

In some embodiments the Ge precursor comprises at least one amine oralkylamine ligand, such as those presented in formulas (2) through (6)and (8) and (9), and the nitrogen reactant comprises NH₃.

Before starting the deposition of the film, the substrate is typicallyheated to a suitable growth temperature, as discussed above. Thepreferred deposition temperature may vary depending on a number offactors such as, and without limitation, the reactant precursors, thepressure, flow rate, the arrangement of the reactor, and the compositionof the substrate including the nature of the material to be depositedon. In some embodiments the deposition temperature is selected to bebetween the temperature where the germanium precursor does not decomposewithout the second nitrogen precursor, at the lower end, and thetemperature where the precursor does decompose by itself, at the upperend. As discussed elsewhere, in some embodiments the temperature may beless than about 600° C., less than about 450° C., less than about 400°C., and in some cases, less than about 375° C. In some embodiments usingGe(OCH₂CH₃)₄ and NH₃ as the germanium and nitrogen reactants, thetemperature is about 350° C.

The processing time depends on the thickness of the layer to be producedand the growth rate of the film. In ALD, the growth rate of a thin filmis determined as thickness increase per one cycle. One cycle consists ofthe pulsing and removing steps of the precursors and the duration of onecycle is typically between about 0.2 seconds and about 30 seconds, morepreferably between about 1 second and about 10 seconds, but it can be onorder of minutes or more in some cases, for example, where large surfaceareas and volumes are present.

In some embodiments the growth rate of the germanium thin films may begreater than or equal to about 2 Å/cycle, greater than or equal to about5 Å/cycle, greater than or equal to about 10 Å/cycle, and, in someembodiments, even greater than about 15 Å/cycle.

In some embodiments the germanium film formed is a relatively puregermanium film. Preferably, aside from minor impurities no other metalor semi-metal elements are present in the film. In some embodiments thefilm comprises less than 1-at % of metal or semi-metal other than Ge. Insome embodiments, the germanium film comprises less than about 5-at % ofany impurity other than hydrogen, preferably less than about 3-at % ofany impurity other than hydrogen, and more preferably less than about1-at % of any impurity other than hydrogen. In some embodiments agermanium film comprises less than about 5 at-% nitrogen, less thanabout 3 at-% nitrogen less than about 2 at-% nitrogen or even less thanabout 1 at-% nitrogen. In some embodiments, a pure germanium filmcomprises less than about 2-at % oxygen, preferably less than about 1-at% or less than about 0.5-at % and even less than about 0.25-at %.

In some embodiments a germanium precursor comprising oxygen is utilizedand the germanium film comprises no oxygen or a small amount of oxygenas an impurity. In some embodiments the germanium film deposited using agermanium precursor comprising oxygen may comprise less than about 2at-% oxygen, less than about 1 at-%, less than about 0.5 at-% or evenless than about 0.25 at-%.

In some embodiments, the germanium film formed has step coverage of morethan about 50%, more than about 80%, more than about 90%, or even morethan about 95% on structures which have high aspect ratios. In someembodiments high aspect ratio structures have an aspect ratio that ismore than about 3:1 when comparing the depth or height to the width ofthe feature. In some embodiments the structures have an aspect ratio ofmore than about 5:1, or even an aspect ratio of 10:1 or greater.

Ge Precursors

A number of different Ge precursors can be used in the cyclicalprocesses. In some embodiments the Ge precursor is tetravalent (i.e. Gehas an oxidation state of +IV). In some embodiments, the Ge precursor isnot divalent (i.e., Ge has an oxidation state of +II). In someembodiments, the Ge precursor may comprise at least one alkoxide ligand.In some embodiments, the Ge precursor may comprise at least one amine oralkylamine ligand. In some embodiments the Ge precursor is ametal-organic or organometallic compound. In some embodiments the Geprecursor comprises at least one halide ligand. In some embodiments theGe precursor does not comprise a halide ligand.

In some embodiments the Ge precursor comprises a Ge—O bond. In someembodiments the Ge precursor comprises a Ge—N bond. In some embodimentsthe Ge precursor comprises a Ge—C bond. In some embodiments the Geprecursor does not comprise Ge—H bond. In some embodiments the Geprecursor comprises equal or less than two Ge—H bonds per one Ge atom.

In some embodiments the Ge precursor is not solid at room temperature(e.g., about 20° C.).

For example, Ge precursors from formulas (1) through (9) below may beused in some embodiments.GeOR₄  (1)

Wherein R is can be independently selected from the group consisting ofalkyl and substituted alkyl;GeR_(x)A_(4-x)  (2)

Wherein the x is an integer from 1 to 4;

R is an organic ligand and can be independently selected from the groupconsisting of alkoxides, alkylsilyls, alkyl, substituted alkyl,alkylamines; and

A can be independently selected from the group consisting of alkyl,substituted alkyl, alkoxides, alkylsilyls, alkyl, alkylamines, halide,and hydrogen.Ge(OR)_(x)A_(4-x)  (3)

Wherein the x is an integer from 1 to 4;

R can be independently selected from the group consisting of alkyl andsubstituted alkyl; and

A can be independently selected from the group consisting of alkyl,alkoxides, alkylsilyls, alkyl, substituted alkyl, alkylamines, halideand hydrogen.Ge(NR^(I)R^(II))₄  (4)

Wherein R^(I) can be independently selected from the group consisting ofhydrogen, alkyl and substituted alkyl; and

R^(II) can be independently selected from the group consisting of alkyland substituted alkyl;Ge(NR^(I)R^(II))_(x)A_(4-x)  (5)

Wherein the x is an integer from 1 to 4;

R^(I) can be independently selected from the group consisting ofhydrogen, alkyl and substituted alkyl; and

R^(II) can be independently selected from the group consisting of alkyland substituted alkyl;

A can be independently selected from the group consisting of alkyl,alkoxides, alkylsilyls, alkyl, substituted alkyl, alkylamines, halide,and hydrogen.Ge_(n)(NR^(I)R^(II))_(2n+2)  (6)

Wherein the n is an integer from 1 to 3;

R^(I) can be independently selected from the group consisting ofhydrogen, alkyl and substituted alkyl; and

R^(II) can be independently selected from the group consisting of alkyland substituted alkyl;Ge_(n)(OR)_(2n+2)  (7)

Wherein the n is an integer from 1 to 3; and

Wherein R can be independently selected from the group consisting ofalkyl and substituted alkyl;Ge_(n)R_(2n+2)  (8)

Wherein the n is an integer from 1 to 3; and

R is an organic ligand and can be independently selected from the groupconsisting of alkoxides, alkylsilyls, alkyl, substituted alkyl,alkylamines.A_(3-x)R_(x)Ge—GeR_(y)A_(3-y)  (9)

Wherein the x is an integer from 1 to 3;

y is an integer from 1 to 3;

R is an organic ligand and can be independently selected from the groupconsisting of alkoxides, alkylsilyls, alkyl, substituted alkyl,alkylamines; and

A can be independently selected from the group consisting of alkyl,alkoxides, alkylsilyls, alkyl, substituted alkyl, alkylamines, halidesand hydrogen.

Preferred options for R include, but are not limited to, methyl, ethyl,propyl, isopropyl, n-butyl, isobutyl, tertbutyl for all formulas, morepreferred in ethyl and methyl. In some embodiments, the preferredoptions for R include, but are not limited to, C₃-C₁₀ alkyls, alkenyls,and alkynyls and substituted versions of those, more preferably C₃-C₆alkyls, alkenyls, and alkenyls and substituted versions of those.

In some embodiments the Ge precursor comprises one or more halides. Forexample, the precursor may comprise 1, 2, or 3 halide ligands. However,as mentioned above, in some embodiments the Ge precursor does notcomprise a halide.

In some embodiments a germane (GeH_(x)) is not used.

In some embodiments alkoxide Ge precursors may be used, including, butare not limited to, one or more of Ge(OMe)₄, Ge(OEt)₄, Ge(O^(i)Pr)₄,Ge(O^(n)Pr)₄ and Ge(O^(t)Bu)₄. In some embodiments the Ge precursor isTDMAGe. In some embodiments the Ge precursor is TDMAGe. In someembodiments the Ge precursor is TEMAGe.

EXAMPLES

The ability to deposit germanium films by decomposing germaniumprecursors at relatively low temperatures was tested. At temperatures ofabout 375° C. and about 400° C., no germanium films were seen when onlyalternating Ge precursor pulses and carrier gas purges without secondreactant. In these decomposition tests, Ge(OEt)₄ was used as thegermanium precursor and was kept at room temperature. The Ge(OEt)₄ wascyclically pulsed through the reaction space for 3 seconds followed by a6 second purge.

However, by utilizing a cyclical deposition process in which thesubstrate was alternately contacted with a germanium precursor and anitrogen reactant, deposition was observed in the temperature range ofabout 350° C. to about 400° C.

In one set of experiments, germanium films were deposited in an F-450®reactor at 350° C. by repeating a deposition cycle comprising alternateand sequential pulses of Ge(OEt)₄ and NH₃. The Ge(OEt)₄ was kept at roomtemperature. The NH₃ was flowed through the reaction space at 100 sccm.Each cycle comprised a 3 seconds germanium precursor pulse, a 6 secondpurge, and a 3 second nitrogen reactant pulse followed by a 10 secondpurge. A thick metal-like film of greater than 80 nm was formed with2000 cycles.

Germanium films were also deposited in an Pulsar® 2000 reactor attemperatures ranging from about 365° C. to about 400° C. using germaniumethoxide (Ge(OEt)₄) as the Ge precursor, and ammonia (NH₃) as thenitrogen reactant. Ge(OEt)₄ is a liquid with a vapor pressure of about0.2 Torr at 55° C. The Ge(OEt)₄ was kept at room temperature. The NH₃was flowed through the reaction space at 100 sccm. Each cycle compriseda 3 seconds germanium precursor pulse, a 5 second purge, and a 3 secondnitrogen reactant pulse followed by a 5 second purge. Each film wasdeposited using a cyclical process of 500 cycles. Composition wasdetermined by Rutherford backscattering spectroscopy (“RBS”). Theresults are summarized in Table 1 below.

TABLE 1 Germanium films achieved with cyclical process. DepositionThickness Atomic Concentration (at %) Sample T (° C.) (nm) Ge O C N 1365 162 95.5 1.5 1.6 1.4 2 375 375 97.8 0.8 0.9 0.5 3 385 493 98.6 0.50.7 0.2 4 400 921 99.2 0.2 0.5 0.1

FIGS. 2A-D show SEM images of the four germanium films summarized inTable 1 above. Accordingly, FIG. 2A is an image of the film deposited ata temperature of about 365° C.; FIG. 2B is an image of the filmdeposited at a temperature of about 375° C.; FIG. 2C is an image of thefilm deposited at a temperature of about 385° C.; and FIG. 2D is animage of the film deposited at a temperature of about 400° C.

FIGS. 3A and 3B show SEM images of two of the germanium films summarizedin Table 1. The image in FIG. 3A is of the film deposited at a reactiontemperature of about 375° C., and the image in FIG. 3B is of the filmdeposited at a reaction temperature of about 385° C. Consistent with thedata of Table 1, FIGS. 3A and 3B demonstrate that there is a temperaturedependence for the growth rate, because the film deposited at about 385°C. is thicker than the film deposited at about 375° C. even though eachfilm was formed using a cyclical process of 500 cycles.

The deposited germanium films exhibited a relatively high sheetresistance of about 4000-9000 Ω/sq.

Although certain embodiments and examples have been discussed, it willbe understood by those skilled in the art that the scope of the claimsextend beyond the specifically disclosed embodiments to otheralternative embodiments and/or uses and obvious modifications andequivalents thereof.

What is claimed is:
 1. A process for forming an elemental germanium thinfilm on a substrate comprising alternately and sequentially contactingthe substrate with a vapor phase germanium precursor and a second vaporphase reactant, wherein the germanium precursor is not a halide.
 2. Theprocess of claim 1 wherein the second reactant is a nitrogen reactant.3. The process of claim 2, wherein the nitrogen reactant comprisesammonia, elemental nitrogen, nitrogen plasma, or nitrogen radicals. 4.The process of claim 1, wherein the germanium precursor is a germaniumalkoxide or alkylamine.
 5. The process of claim 1, wherein the germaniumprecursor is tetravalent.
 6. The process of claim 1 further comprising,after contacting the substrate with the vapor phase germanium precursor,exposing the substrate to a purge gas and/or a vacuum.
 7. The process ofclaim 1 further comprising, after contacting the substrate with thevapor phase second reactant, exposing the substrate to a purge gasand/or a vacuum.
 8. The process of claim 1, wherein the germaniumprecursor at least partially decomposes on the substrate surface.
 9. Theprocess of claim 8, wherein the process is performed at a temperaturebelow the temperature at which the germanium precursor decomposeswithout the presence of another precursor.
 10. The process of claim 1,wherein the elemental germanium thin film comprises less than about 5at-% impurities.
 11. The process of claim 1, wherein the germaniumprecursor is not a germane.
 12. The process of claim 1, wherein theprocess is performed at a temperature below about 500° C.
 13. A vapordeposition process for forming an elemental germanium thin film on asubstrate in a reaction chamber, the process comprising: continuouslyflowing a first reactant through the reaction chamber, contacting thesubstrate with a vapor phase germanium precursor, wherein the germaniumprecursor is not a halide, removing excess vapor phase germaniumprecursor and reaction by products, if any, from the reaction space, andrepeating the contacting and removing steps while flowing the firstreactant through the reaction chamber until an elemental germanium thinfilm of the desired thickness has been formed.
 14. The process of claim13, wherein the concentration of the first reactant is kept low enoughto suppress any gas-phase reaction between the nitrogen reactant and theGe precursor.
 15. The process of claim 13, wherein the first reactant isa nitrogen reactant.
 16. The process of claim 13, wherein the germaniumprecursor is an alkoxide.
 17. The process of claim 13, wherein the vaporphase germanium precursor is tetravalent.
 18. A deposition process forforming an elemental germanium thin film on a substrate in a reactionchamber the process comprising one or more deposition cycles comprising:contacting the substrate with a first vapor phase germanium precursor;removing excess vapor phase germanium precursor; contacting thesubstrate with a second vapor phase reactant; removing excess secondvapor phase reactant; and repeating the contacting and removing stepsuntil an elemental germanium thin film of the desired thickness has beenformed on the substrate, wherein the first vapor phase germaniumprecursor is not a halide, and wherein the second reactant does notcomprise H₂ or H₂-based plasma species.
 19. The process of claim 18,wherein the elemental germanium thin film comprises less than 5%impurities.
 20. The process of claim 18, wherein the second vapor phasereactant comprises nitrogen.